The objective is to study the mechanism of immunologic stimulation of cytomegalovirus (CMV) infection in man and to seek laboratory evidence of transmission of CMV in humans by transplanted kidneys. Chronic mouse CMV infection will be accentuated by cyclophosphamide and allogeneic graft reaction. Attempts will be made to do the same in a model of latent CMV infection. Viral stimulation in these two models will be compared by identifying the infected cell, development of viral antigen and viral genome monitored by immunofluorescence and nucleic acid cytohybridization. Models of immunologic stimulation and activation of latent virus by immunosuppressants will be studied in defined cultures of immunocytes and non-immunocytes. In a prospective study of kidney transplant recipients, evidence of human CMV and methods to activate it will be sought in kidney specimens obtained (when available) by biopsy, nephrectomy or autopsy. Specimens of kidney will also be obtained from donors (when available) and at autopsies of children and adults. By comparing antibodies of donor and infected recipients with agents isolated, evidence of transmission of virus from the donor to the recipient and the nature of specific strain humoral immunity to CMV will be sought.